1. Field of the Invention
The present invention relates to a method and apparatus for measuring the weight of a vehicle while the vehicle is in motion. The present invention incorporates a simple, low cost portable device for weighing vehicles that also does not require the vehicles to stop during the weighing process. The apparatus to which the present invention relates is in the field of Weigh-In-Motion devices.
2. Description of the Prior Art
Weigh-In-Motion devices are particularly applicable for weighing a moving truck while it travels down a road. At present, trucks are weighed in weighing stations. The use of weighing stations poses several problems: (1) They are easily visible which allows truckers to avoid them; (2) They are very costly to build and operate; (3) Their use slows truck traffic severely; and (4) All trucks must pass over the scale as it is impossible to distinguish between loaded and overloaded trucks prior to weighing.
The alternative approach to the weigh station is a Weigh-In-Motion device. There are several such devices in application at the present time. Conceptually, the technologies presently used in Weigh-In-Motion devices are as follows:
(1) STRAIN GAUGE--Several types and configurations are possible including capacitance and resistance gauges of the weldable or adhesive bonded type. Typically, the strain, resulting from the application of an unknown force such as a truck, is applied to a plate or beam and then measured. The force is calculated from the known bending characteristics of the beam or plate.
(2) PIEZOELECTRIC--In this application, a mechanical or pneumatic force is applied to a crystal and this produces a rate proportional charge. The charge is converted to voltage by a charge amplifier and this is used to measure weight.
(3) CAPACITANCE--Parallel plate capacitors exhibit approximately linear changes in total capacitance as the plate spacing changes. The change in capacitance is related to the applied force by a spring rate. This typically requires a high frequency excitation for a reliable output.
(4) LINEAR VARIABLE DIFFERENTIAL TRANSFORMER--These typically consist of a linear transformer with a moveable core. As the core is displaced by the bending of a beam or plate under load, the output voltage of the transducer varies proportionally due to changes in inductance. These further require a carrier amplifier for signal conditioning. There are several major drawbacks to prior art devices which embody the above enumerated concepts. In most cases, the force measuring lattice, whether it be Strain Gauge, Piezoelectric, or Linear Variable Differential Transformer type, must be embedded in the road. The Capacitance type may lay over the roadway but is relatively thick, for example greater than 1/2 inch, and can distort the measurements due to wheel dynamics. This requires a high initial cost to install such a device. In addition, must devices are not readily portable. If the device is moved to another location, there is a considerable expense involved in repairing the road after removal. In the event a problem arises with the device, it requires a significant effort to remove the device for repair and this further restricts the use of the highway or other roadway while that portion of the road is torn up to repair or replace the device. In addition, available devices are relatively costly ($20,000.00 to $200,000.00).
There are several prior art United States patents which address the subject of Weigh-In-Motion systems. They are as follows:
(1) U.S. Pat. No. 4,339,010 issued to Malikov, et. al. for "Apparatus For Weighing Transport Vehicles in Motion."
(2) U.S. Pat. No. 4,317,496 issued to Krause for "In Motion Weighing System."
(3) U.S. Pat. No. 4,049,069 issued to Tamamura et. al. for "Device For Weighing Running Vehicle."
(4) U.S. Pat. No. 3,835,945 issued to Yamanaka et. al. for "Device For Weighing Running Vehicle."
(5) U.S. Pat. No. 3,825,734 issued to Jacobs et. al. for "Monitor For Moving Vehicles."
(6) U.S. Pat. No. 3,679,011 issued to Hawver et. al. for ""Weighing Scale Assembly."
(7) U.S. Pat. No. 3,601,209 issued to Paelian for "Vehicle-Weighing System."
All of these prior art patents basically incorporate one or more of the above described measuring systems, with all of their attendant problems. The Malinkov et. al. patent embodies an apparatus for weighing transport vehicles in motion, wherein at least two measuring units are electrically connected with a recording unit, each comprising a load platform which bears on a dynametric pickup load cell at a supporting point and is connected to a supporting structure by means of four rods installed in pairs at two sides of the load platforms. The weight of the vehicle bears on the load platform which in turn bears on the load cell at a geometric point whose vertical displacement due to an arbitrary moment of forces acting upon the load platform causes a measurable deformation of the rods.
The Krause Patent is concerned with a system for weighing a plurality of coupled railroad cars. The system uses preselected photocell sensor units in an arrangement keyed to the cross section bulk of each car. The shape of the cars interrupts photocell signals at predetermined points on a weigh bridge, thereby actuating means at the precise point when each car is at the optimum weighing position on a scale.
The Tamamura et. al. patent discloses an apparatus for measuring the weight of a moving vehicle which includes a series of platforms with the length of each platform being shorter than the distance between the axles of the vehicle. The displacement of the platforms is converted to electrical signals and electronic averaging of the signals produced by the individual axle loads enables the measuring instrument to determine the weight of the vehicle.
The Yamanaka et. al. Patent discloses another device for electronically measuring the weight of a moving vehicle as it passes over a platform.
The Jacobs et. al. Patent discloses another apparatus for weighing vehicles through utilization of digital scales used in conjunction with load cells.
The Hawver Patent discloses an apparatus which measures the weight of a moving vehicle such as a railroad car through the use of a weigh bridge over which the vehicle passes. The load applied to the weigh bridge is imposed on load cells.
Finally, the Paelian et. al. Patent discloses an apparatus for weighing a moving vehicle through a plurality of adjacent but independent weighing platforms when the wheel passes over one or more of the weighing platforms.
Therefore, all of the known prior art embodies an application for weighing a moving vehicle which incorporates either weighing platforms, load cells, or a combination of the two. These can be used in conjunction with the previously described methods of strain gauge, piezoelectric, capacitance and linear voltage displacement transducer. These are usually bulky in construction and if incorporated into a system for measuring the weight of a vehicle such as a truck as it passes along a roadway, the system must be embedded into the roadway with all of the previously dicussed problems.
None of the prior art embodiments incorporate a simple, inexpensive, portable method and apparatus for weighing a vehicle in motion.